This is a bit of a mess. It starts out as one kind of movie, then slowly drifts into being a different kind of movie, and it never really connects.

Dave is a policeman who, despite 17 years on the force, seems singularly ill-suited to the job. Emotionally stunted, he's been demoted to manning the police kiosk in a hospital. One night Hon, also known as "Demon King" and the leader of a cult of bank robbers, stumbles into the hospital after violently avoiding being caught by the cops, and Dave just happens to be the right blood type to save Hon's life. Though Dave's contribution to saving a cop-killer is completely unintentional, he gets chewed out by the (rogue) cops who were hunting Hon.

Hon is in custody at the hospital (though apparently the police can't charge him with anything), but he basically uses an escape plan cribbed from the Joker and is soon committing another ultra-violent jewel heist. But he stiffed the rest of his gang on the last heist, and he goes over a cliff when they betray him this time.

Dave, meanwhile, has been reassigned to a street beat, and things aren't going well. We now find out that he has violent mood swings and flagellates himself in the privacy of his apartment. Hypnosis is used to try to get to the root of his problems, but he goes out at night and clandestinely meets with the very alive Hon, who helps him turn his old gang members against each other.

It's tough to talk to much about the movie without major spoilers, but beyond some startling action scenes, the rest of the movie is mess. It reminds me of those "psychological thrillers" like Basic Instinct and its imitators, but replacing sex with violence. Psychological plausibility and tight plotting are not the priority.